1. Field of the Invention
The present invention relates to an exposure control apparatus for use in a photographic camera with interchangeable lenses.
2. Description of the Prior Art
There is already known, for exposure control in the single lens reflex camera with interchangeable lens employing the through-the-lens (TTL) light measurement, an exposure control apparatus capable of so-called automatic programmed exposure in which the diaphragm aperture of the lens is automatically regulated in response to a program value determined according to the brightness of the object. Also there is known such exposure control apparatus in which the measured output of the light from the object coming through the adjusted diaphragm aperture and the output of position detecting means for a diaphragm adjusting member are used as the input signals for a shutter speed calculating circuit to obtain a shutter speed corresponding to the adjusted diaphragm aperture.
In case of using the single lens reflex camera having such through-the-lens (TTL) exposure control apparatus with interchangeable lenses of different maximum diapragm apertures, the camera is required to identify the maximum diaphragm aperture of the lens used in order to obtain a same combination of a diaphragm aperture and a shutter speed for the object of a determined brightness regardless of the maximum aperture of the lens and such requirement is achieved for example by the invention of the present applicant disclosed in the U.S. patent application Ser. No. 971,825 or German patent application No. DT P2,856,307.7 corresponding to the Japanese Patent Laid-Open No. 54-78127.
For this purpose each interchangeable lens for use in the camera having such exposure control apparatus is required to have a specific signal member for transmitting the maximum lens aperture to the camera as a direct signal or an indirect compound signal in combination with another signalling member.
For the convenience of customers, the interchangeability of a new lens or camera with those already in the market is a major concern for a camera manufacturer, and it is strictly undesirable to provide a new camera not allowing the use of the interchangeable lenses sold before. For this reason, in case a manufacturer having sold interchangeable lenses not provided with signalling means for the maximum lens aperture provides a new lens-interchangeable camera with the above-mentioned exposure control, it is desirable to allow the customers to use said new camera in combination with the interchangeable lenses already sold, but such objective has not been achieved in the prior art.